DESCRIPTION: (Applicant's Abstract) In the basal ganglia, dopamine, through binding to D1 receptors, increases cAMP levels leading to activation of cAMP-dependent protein kinase (PKA) and phosphorylation of a family of substrates, termed DARPPs (for dopamine and cAMP-regulated phosphoproteins). Our studies have indicated that members of the DARPP family are likely to mediate many of the actions of dopamine in this brain region. There is also considerable evidence to indicate that the actions of psychomotor stimulants (e.g. cocaine and amphetamine) are mediated through augmentation of neurotransmission in mesolimbic and nigrostriatal dopamine systems. The major aim of the present proposal will be to study the role of two of the DARPP family, namely DARPP-2l and DARPP-16, in the actions of psychomotor stimulants. Specific Aims will be: 1. to use mice in which either DARPP-16 or DARPP-21 has been "knocked-out," to examine the role the proteins play in dopaminergic neurotransmission, and in the actions of psycho stimulants. 2. Our studies have implicated DARPP-16 in mediating an effect of the neurotrophin, nerve growth factor, on GAP-43 mRNA stability, and protein expression. Neurotrophins are potential targets for cocaine-induced gene expression, and may contribute to the biochemical and behavioral actions of cocaine. We will characterize the role that phosphorylation ofDARPP-16 has in the regulation of GAP-43 mRNA stability, and establish the structural basis for the interaction of DARPP-16 with GAP-43 mRNA. We will also characterize changes in gene expression in wild type and DARPP-16 knockout mice, under basal conditions and following treatment with cocaine. Studies of gene expression in DARPP-21 knockout mice will also be carried out. 3. Our recent studies have indicated that the neuronal cyclin-dependent kinase, cdk5, may play an important role in the actions of psychostimulants (see Project 1). We have found that DARPP-16 is also phosphorylated at novel site(s) by cyclin-dependent protein kinases, including cdk5. We will continue to study phosphorylation of DARPP-16 by PKA and cyclin-dependent protein kinases. The characterization of basal ganglia phosphoproteins, within specific neurons, which are affected by psychostimulants, will provide a rational new approach to developing drugs that specifically affect these phosphoproteins or their targets. Thus, these studies may have potential implication in the development of new therapeutic approaches to the treatment of such drugs of abuse.